1. Field
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred on (part of) the substrate (e.g., a glass plate), e.g., via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
Instead of a circuit pattern, the patterning means can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can comprise a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate can be rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or which covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through the projection beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. The substrate is disposed on a substrate exposure table or stage, during a scanning process. Unexposed substrates, i.e., those substrates that are not yet been subject to exposure, are stored in a storage device or system. A robot loads the unexposed substrates to the exposure table where they are subsequently exposed. After exposure, the exposed substrates are returned to the storage by the robot.
Lithographic apparatuses include a clean air supply which distributes clean air into the lithographic apparatus. The clean air is provided in order to maintain a clean environment within the apparatus, since contamination within the apparatus leads to imaging errors. In these lithographic apparatuses a down flow of clean air is provided by clean air supply units, which can be located in the apparatus.
In certain applications, the substrates used, for example, in the manufacture of flat panel displays, are relatively large. For example, they can have an area in excess of 1 m2. It has been found that because of the relatively large image area, particle contamination is a problem. This is a particular problem for the unexposed substrates. As mentioned above, clean air is directed from above. It has been found that due to the arrangement of the substrate table and its interaction with the robot, the clean air does not efficiently reach the unexposed substrate prior to exposure. This leads to imaging errors. Furthermore, another consequence, in applications where the substrates and substrate tables are relatively large, is that the movement of the tables within the limited space of the apparatus in loading and unloading the substrates act as pumps, which can “pump” contamination particles onto the unexposed substrates. Furthermore, the moving robot gives rise to wake effects, and thus under pressure zones above the unexposed substrate, which also constitute a risk of contamination.
Therefore, what is needed is a system and method to reduce the risk of contamination within a lithographic apparatus. For example, it is desirable to reduce the risk of contamination of an unexposed substrate.